The goal of the initial distribution system evaluation (IDSE) is to identify the sites in the distribution system where customers may be exposed to high levels of DBPs. These sites will then be used for Stage 2 compliance monitoring. NTNC water systems serving less than 10,000 population are exempted from IDSE requirements but will be required to do Stage 2 compliance monitoring.
Systems had a choice of four IDSE options:
- Standard Monitoring: Monitoring takes place over one year.
- Systems Specific Study: Uses existing monitoring data or hydraulic modeling.
- 40/30 Certification: Uses existing data if all results are < 1/2 the MCL.
- Very Small System Waiver: Available to water systems with less than 500 population.
Those systems that chose Standard Monitoring must complete the IDSE monitoring and reports according to the dates in Table 1
. New water systems that add a disinfectant other than UV and existing systems that begin adding a disinfectant must consult with Drinking Water Services to determine IDSE compliance requirements.
Systems that were able to utilize either the 40/30 certification or very small system waiver are required to complete a Compliance Monitoring Plan (CMP) before compliance monitoring begins, but otherwise have no other requirements under the IDSE portion of the rule.